The present invention relates to improvements in communications between communication devices using different protocols and in particular rail car data communications.
Data communications in the field of communications, including data communications between rail cars are generally transmitted in a bit serial communication format through a network. Typically data is transmitted in a network between two data endpoints and the data is packaged according to specific data communications protocols so as to facilitate transmission of the data across the particular network. The particular packaging may include network management and other information such as headers and trailers to the information transmitted to facilitate transmission of the data based on the requirements of the particular protocol that is being used. Framing is a term that is used to describe the packaging of data by a protocol for transmission.
There are a number of different protocols available for data transmission. Some of these protocols may include data transmission using time division multiplexing (TDM) approaches using standards such as T1 and E1 which are well known in the art. Another example standard may include high level data link control (HDLC) or asynchronous transfer mode (ATM). Each of these protocols are used in their own types of applications and have goals in terms of history, performance, error immunity, flexibility and other factors that creates preferences for one over another protocol. As a result, each of these protocols employ framing procedures by which data is packaged for transmission across the various networks in which they are employed. For the most part these protocols are generally incompatible and require that there be a translation or conversion to transmit data in a transmission link that employs two or more protocols in two or more segments of the communication path.
Operating systems in rail cars are becoming increasingly sophisticated. In many instances microprocessors are commonly used to control various operational functions. In addition, communication systems in these rail cars have also become relatively advanced, particularly in the area of car to car and passenger communication systems that permit telephone communications between the moving rail car and wireless base stations or land lines.
The communications systems in rail cars typically employ a E1/T1 transmission system. A problem arises when additions are made to the communications system that do not employ the E1/T1 protocol for communicating. For example, a user may attempt to add an off the shelf hardware such as a computer, modem or other device that does not use the E1/T1 protocol. Many of these off the shelf hardware device use serial channels (Com ports) that employ asynchronous TTY type formats, i.e., a start bit, 5 through 8 data bits, one or two stop bits and some parity bit options. When hardware that is not compatible with the E1/T1 protocol is added there can be significant downtime to equipment before it is realized by the installer that there is an incompatibility and in attempting to correct the incompatibility between the added hardware and the system currently in use. One reason why off the shelf hardware is attractive to the transit system running the rail cars is the cost savings that arises from the ability to use an item that is off the shelf as opposed to one that is not. When the savings are multiplied across a fleet of rail cars the savings to the transit authority can be significant. Another advantage to off the shelf hardware is the availability of replacements in the event of a failure of a part. The off the shelf items are usually available from a variety of convention sources thus reducing a car""s down time waiting for parts delivery.
It is an object of the invention to permit a synchronous communication system to communicate with an asynchronous communication system.
It is an object of the invention to provide an interface device to permit a synchronous communication system to communicate with an asynchronous communication system.
It is another object of the invention to permit a communication system using an E1/T1 protocol to communicate with a communication system using a non E1/T1 protocol.
It is an object of the invention to permit an E1/T1 based communications system to communicate with non E1/T1 based hardware having a universal asynchronous receiver transmitter.
It is a still further object of the invention to permit a rail car having a communication system using an E1/T1 protocol to communicate with a communication system using a non E1/T1 protocol.
The present invention is primarily directed to rail car communication system and in particular communication system used to transfer data and voice communications from one car to another. The present invention has particular applicability for use in subway cars. However, one skilled in the art will appreciate that the teachings of the present invention are pertinent to other types of communication systems besides those used in rail cars.
According to the present invention a communication system using an E1/T1 protocol is provided with an interface device, which translates data received from hardware device having, inter alia, a microprocessor and a universal asynchronous receiver transmitter (UART) used for serial communications such as COM 1-4. The transmitter can be a typical UART that is commonly found on conventional personal computers (PC""s). The asynchronous UART data is interfaced with the E1/T1 channel. E1/T1 communications is usually done on a byte (8 bits) by byte basis but the present invention uses bit by bit communications instead of the byte by byte transmission. Additionally, data is normally sent at the data rate of the E1/T1 channel not some other unrelated speed such as those used by a UART during serial communications. Also, the data is usually sent synchronously, like the E1 channel, not asynchronously, as with a UART.